Throughout history, surveyors and mapmakers utilized immovable objects or monuments as reference points for the generated survey or map. Although these monuments were generally thought to be immobile, it has recently been determined that, due to the shifting of the earth's crust and similar movements, the actual latitude/longitude coordinates of these monuments have changed. The utilization of satellite positioning systems has indicated that several of these long-standing monuments have moved, in some cases several miles, since the initial determination of their latitude/longitude coordinates. Therefore, errors could result in constructing a survey or a map without periodically updating the exact latitude/longitude coordinates of the monuments.
Additionally, it has been determined that the present method of creating a map results in a map which is accurate to 50 feet in the center of the map and to 200 feet on the outside edges of the map. The reasons for these inaccuracies are not only due to the employment of inaccurately designated monuments, but rather to the methods utilized to create the modern-day map. Typically, maps have been created by aerial photography techniques, whereby an airplane would canvas, and take a plurality of photographs of, a certain geographic area. The largest inaccuracy resulting from this technique was that the angle of the camera and the lens utilized referenced to the surface of the earth would create distortions. This was true regardless of whether an actual or an infrared picture of the area was taken. Additional inaccuracies resulted since a flat map was created from a curved surface, thereby causing an inherent distortion of the map.
This aerial photography technique has largely been replaced by orbiting or geostationary satellites. The orbiting satellites would take a single sweep across an area, record an image and then take additional scans over adjacent areas, and images are produced in a manner such as that displayed on a television screen. However, regardless of the fact that a digitized image was being produced, a flat map was still being produced from a curved surface. Additionally, since the orbiting satellite was moving at a relatively great speed, further inaccuracies resulted. While a geostationary satellite would not produce inaccuracies due to the movement of the satellite relative to the earth, distortions due to the curvature of the earth were still produced.
Generally, if the mapmaker's purpose was to create a road or terrain map where the relative positions of roads, towns or physical formations were important, the distortion inaccuracies inherent in the mapmaking procedure were relatively unimportant, as long as the relative positions were consistent. However, quite recently, the need for tracking a particular vehicle and displaying the position of the vehicle on a digitized map more accurately than the distortion factor produced by state-of-the-art maps has been recognized. The Assignee of the present invention has developed a system, described in U.S. Pat. No. 4,651,157 for tracking a vehicle. One of the purposes of the invention described in the aforementioned patent was to quite accurately track the position of a vehicle, such as a police car, taxi, ship or similar vehicle or vessel, as it traverses city streets or marine channels and rivers. The patent describes a system in which a computer-generated digital map is provided on a display screen, and the position of the tracked vehicle is projected onto this map. Quite obviously, if the particular map is accurate to only 50 feet, the position of the tracked vehicle would not be accurately displayed on the projected map. Instead of the position of the automotive vehicle being properly shown on a particular street or road, the map might indicate that this vehicle is in the middle of a field or within a permanent structure, such as a building.
Therefore, a method of accurately displaying the position of the vehicle on a map, regardless of the inherent inaccuracy of the produced digitized map, has been developed. This display technique would then be able to be utilized in conjunction with the tracking system described in U.S. Pat. No. 4,651,157.
The above-noted method and system is described in U.S. patent application Ser. No. 801,612, now U.S. Pat. No. 4,791,572 filed on Nov. 20, 1985 which describes a method of displaying the position of various vehicles or vessels on a generated map much more accurately than any known method of display, regardless of any distortion or error produced by the map itself.
Initially, a digitized street or terrain map is produced utilizing state-of-the-art techniques and inputted into a computer provided with a display screen. Before the digitized map is displayed, the exact coordinates of a plurality of reference monuments are determined utilizing various known techniques, such as laser surveying. The exact coordinate system employed in the present invention is unimportant as long as a consistent system is used. For the sake of simplicity, the invention will be further described with respect to a latitude/longitude coordinate system, although it is noted that the state plane coordinate system, or any other coordinate system, could be utilized. Thereafter, the exact latitude/longitude coordinates of the reference monuments are inputted into the computer's memory in the form of a table of geographical reference coordinate data referenced to the digitized map, thereby allowing the exact position of the reference monuments to be displayed on the digitized map. Although this table of data is not generally used to produce a map to be displayed on the computer screen, if this information were to be used to produce a map, this map would be composed of a first series of parallel lines and a second series of parallel lines perpendicular to the first series of parallel lines. After this information has been provided to the computer, the position of each of these reference monuments is determined by navigational tracking techniques such as the land or sea-based LORAN-C Navigational System. Additionally, it should be noted that any navigational system from which positional information can be derived could be used with the method of the present invention. These systems could be used with air-borne transmitters carried aloft by balloons or ultimately, satellites may be employed for this purpose. The latitude/longitude coordinates determined by the navigational system utilized are compared to the exact latitude/longitude coordinates previously discovered. Since it is quite unlikely that these two sets of coordinates for each of the monuments would be equal, a correction factor is derived based upon these sets of coordinates. This correction factor is inputted into the system computer.
Utilizing the LORAN-C information received for all of the monuments, a table of positional data is produced bridging the digitized map with the latitude/longitude map. This table is inputted into the system computer. Although this table of data is not generally used to produce a map to be displayed on the computer screen, if this information were to be used to produce a map, the map would be composed of a plurality of parallel curved lines formed in a grid-like pattern. The correction factor previously determined is used to update the table of positional data previously compiled and would then effectively distort or skew the aforementioned plurality of parallel curved lines which would be produced if the positional data would be used to produce a displayed map in such a manner that each of the monuments would be precisely displayed at its actual location on the displayed digitized street or terrain map. At this point, the method of the present invention would display the position of a tracked vehicle more accurately than has been presently accomplished.
However, the position of the tracked vehicle can be displayed still more accurately by dispatching various vehicles which are in communication with the central station and traverse the geographical area to be mapped and displayed. As previously implied, both vehicles or vessels can be utilized and tracked, but for simplicity, the term vehicle will be construed to include vessels or even aircraft. These vehicles are in voice communication with the monuments or a central station, verbally indicating the exact physical position of the vehicle to the central station as well as transmitting navigational tracking information received by LORAN-C transmitters to the central station.
This newly received information is used to produce a second correction factor by comparing the exact physical location of each of the vehicles with the position of the vehicle determined by the standard LORAN-C navigational techniques known in the art. This second correction factor is used to again update the table of positional data and this data is used to produce a transparent layer map, and then the curved grid lines produced by such a map would be distorted and skewed, but the position of the vehicles would be correlated with the latitude/longitude coordinate system to accurately display the position of the vehicle on the street or terrain map.
In operation, any vehicle being tracked by the system of the present invention would be accurately displayed on the street or terrain map by positioning the vehicle on the distorted and skewed transparent layer map and then projecting this position onto the street or terrain map. Since the LORAN-C signals received from the LORAN-C transmitters by the monuments are constantly being distorted, the exact position of each monument is constantly compared to the position of each monument determined by the LORAN-C triangulation techniques and additional correction factors are continually being derived. These factors are used to distort or skew the grid lines of the transparent layer map even further, and it can be shown that this map is virtually in a constant state of flux. Alternatively, this additional information could be used to slightly distort or "rubber sheet" the digitized street or terrain map without altering the transparent map.
While the system described hereinabove produces a very accurate map, a method is still needed which can be utilized to update the information initially displayed on the map. For example, a method is needed to input information based upon newly-created landmarks, streets, subdivisions and the like. Additionally, a method must be developed in which incorrect or outdated information provided on the map can be changed to correctly display the proper information on the map.
Furthermore, a method must be developed in which a digital map can be "conflated" with a second map provided with additional information. This conflation technique would be especially appropriate in situations where it is required that the digital map contain address or zip code information correlating the particular position on the map with its respective address range or zip code.
Additionally, a method must be developed in which the information relating to the particular location of each of the vehicles can be displayed in tabular form on the display. This information can be displayed regardless of whether the first digital map is conflated with a second map or whether the conflated map has been updated. Furthermore, a method must be developed in which information provided in the conflated map relating to particular addresses, vehicle locations, and landmark locations are displayed in a tabular manner.